The International Telecommunications Union (ITU) has introduced the G.709 standard for “Interface for the Optical Transport Network (OTN)”. This standard includes a set of recommendations by the ITU and provides for data to be transmitted in specific frames, each of which including a header.
G.709 includes recommendations directed toward networks in which multiple users transmit traffic over one or more portions of the same network. For example, a link including four nodes connected in series may carry traffic for a first user between the first and second nodes only, while a second user may transmit traffic from the first to the fourth nodes. In order to permit monitoring of each user's traffic, G.709 specifies that up to six Tandem Connection Monitoring (TCM) fields be provided in each header, such that each of up to six users is assigned a corresponding TCM field. The TCM fields can be processed at each node along a link carrying the traffic of a particular customer and terminated at end point nodes of the link. In addition, TCM fields may be used to designate portions of a network that may be monitored or controlled independently of each other.
Data carried in each TCM field may be calculated based on one or more parameters. One of these parameters is the propagation delay between nodes along the link. Conventionally, in order to determine the propagation delay, an initiating or initiator node sends a predetermined series of bits for each TCM to a peer node. The peer node, in turn, stores information indicative of the timing of the received bits for subsequent transmission back to the initiator node. As noted above, there may be up to six TCM fields in a given header, and, therefore, additional memory may be required in the peer node in order to store the timing-related information for each TCM field. If more TCMs are provided, the amount of storage or memory for storing such data would necessarily increase accordingly. Alternatively, the propagation delay may only be determined in connection with a single TCM field.
Moreover, propagation delay calculations are typically carried out by software, which may require a relatively long time to perform such calculations.
Accordingly, a simpler approach to determining propagation delay that is faster and requires less peer node memory is desired, for example, in a G.709 compliant network.